question on used Class II FDA device ownership

If I want to buy a class II device such as an Acutron Mentor or an Alpha Stim and I get one USED. Where do I stand with the FDA? I mean these are Class II devices. I can't make sense of the FDA language and the modernization act?? I don't want to risk the money until I know if I can keep it. The pop up from time to time on the net. Does any one know the facts? Tweet